1. Field of the Invention
The present invention relates to a laser level, and in particular to a laser level with temperature control device for compensating adverse effects brought to the absolute measurement accuracy of a tilt sensor of the laser level by temperature drift, and a temperature control method thereof.
2. Description of Prior Art
A laser level utilizes the characteristic of excellent linearity of laser beams to measure or verify a horizontal line/surface or a vertical line/surface by a laser beam emitted by a laser emitter. Because of convenience in use and increasingly affordable cost, the laser levels are accepted by users and have been widely used in the constructing or assembling process of construction projects and large machines. U.S. Pat. Nos. 5,914,778, 6,762,830 and 7,013,571 each disclose a conventional laser level.
However, it has been found that tilt sensors incorporated in most laser levels encounter with the problem of temperature drift with ambient temperature changes, which adversely affects measurement accuracy of the laser level. Currently, two solutions have been proposed to address this problem. One is to indicate to the user in the laser level specification or relevant product documents that the specified measurement accuracy of the laser level is a relative accuracy at approximately the same ambient temperature conditions, not the absolute accuracy within the operating temperature range of 0° C.-40° C. In addition, the temperature drift coefficient will be provided in the specifications. For example, the measurement accuracy is 0.01° C., and the temperature drift coefficient is 0.01°/° C. This solution helps the user roughly evaluate the measurement accuracy of the laser level according to the ambient temperature at measurement time, but provides no substantial aid in increasing the measurement accuracy of the laser level. Another solution is to provide compensation for temperature drift so as to increase the measurement accuracy. Reading values of the tilt sensor at different temperature points are first recorded in the form of a lookup table, and then temperature drift compensation is performed by software functions. By this method, the measurement accuracy of the laser level can be increased. However, the number of temperature points measured in factory for calibration is limited. Thus, it cannot be promised that a corresponding calibrated value can be found in the lookup table for every temperature variation in practical use. Accordingly, a certain accuracy tolerance still exists.